1-List down the applications of auxiliary DC power supply system in Power plants?
- Protections relays
- Circuit breakers
- Trip circuits
- Telephone system & communication
- Emergency lighting
- Transmitters & Positioners
- Emergency oil pumps
- Metering panels
2-List down the various DC voltages & their applications in power plants
220 VDC & 110 VDC
Trip & closing coil of circuit breakers
+/- 24 VDC
3-What is the power source for DC supply?
Main power source is lead-acid storage battery & AC/DC rectifier set
4-What are the installation requirements for lead acid battery ?
- The room should be isolated from other system
- Room should have adequate lighting & ventilation
- The room walls & floor should have acid proof tiles
- Battery cells should be installed on insulated racks
- Racks should be placed on insulator generally porcelain insulators
- Cables should be acid proof
- The DC bus bars should be of round or flat copper materials
- Bus bars connections are made by soldering or brazing
- The positive terminal of the battery is Red & negative terminal should be blue
5-How do you calculate the maximum discharge current of batteries?
Maximum discharge current = (Continuous load (W1) + Short time Load (W2)) / Rated Voltage
6-How do you specify the batteries?
Batteries have following specification:
- Rated voltage
- No.of cells
- AH capacity
- Arrangement of cells
- Details of charging equipment
7-What do you mean by AH of batteries?
AH (Ampere hour) is the capacity of battery. It is the product of current and total time required for discharge. It depends on the magnitude of discharge current.
8-How do you decide the number of batteries for a particular battery bank?
No. of battery cells = Bus bar voltage / Voltage of one cell
9-What are the various charging methods employed for batteries?
- Initial charging
- Quick charging
- Trickle charging
10-What do you mean by trickle charging? & what is its significance?
Trickle charging is constant charging current that is supplied to battery to compensate its discharge current.
Batteries get discharge when not in use. Hence to avoid sulphating, the batteries should be kept continuous charging by trickle charging.
11-What do you mean by primary cells (dry cell) & secondary cells?
Primary cells are non rechargeable cells & Secondary cells are storage batteries
12-What are anode, cathode & electrolyte in Lead-acid batteries?
- Cathode: Sponge lead
- Anode: Lead Peroxide (PbO2)
- Electrolyte: Sulphuric acid & water
13-What is the voltage level of lead acid batteries that are generally employed?
It is 2 V
14-What is the voltage level of fully charged & fully discharged lead acid battery?
Voltage of fully charged cell is 2.5 V & 1.75 V for fully discharged cell
15-What will happen during battery discharge & charging of lead acid battery?
During discharging process, the lead & lead peroxide het change into lead sulphate. And during charging lead sulphate gets convert into lead & lead peroxide
16-How do you check the specific gravity (SG) of electrolyte of lead acid battery?
Specific gravity (SG) is checked with the help of Hydrometer
17-What is the SG of fully charged & fully discharged electrolyte
SG Fully charged electrolyte: 1.28 & 1.12 for fully discharged electrolyte
18-What is the proportion of Sulphuric acid & water in Lead acid batteries?
Sulphuric acid: 64% & Distilled water: 36%
19-How do make up electrolyte level in lead-acid batteries?
Lower level of electrolyte is due to evaporation of water.
If the lower electrolyte level is due to evaporation of water, then add distilled water. And if If the lower electrolyte level is due to spilling over bubbling, then add acid & water solution.
20-Explain the charging method of lead-acid battery?
During charging process current forced into battery from opposite direction to its normal direction of current flow.
That is during normal use current leaves from positive terminal & enters through negative terminal. During charging current enters through positive terminal & leaves through negative terminal
21-Why do the lead-acid batteries get discharge when they are not in use?
This is because internal discharge current due to impurities in the electrolyte
22-What electrolyte is used in Nickel-Iron batteries?
23-What is the voltage level & density of electrolyte of Nickel-Iron battery?
It is 1.2 V & 1.2
24-Which electrolyte is used for Nickel Cadmium batteries?
25-What precautions do you take to avoid over discharging of battery?
- Over discharging can be avoided by
- Regular charging of battery
- Avoid excessive discharge rate
- Avoid short-circuit currents & leakage current
- Schedule charging & discharging
- When not in use, battery terminals should be considered
26-What do you mean by sulphated Battery?
Discharge battery with abnormal hardened lead sulphate on its plate is a Sulphated battery
27-What actions you will take if Battery is charging slowly?
- Check battery connections & rectify if there are loose connections
- Check charger capacity
- Add distilled water or acid water solution if electrolyte is low
- Check sulphatation of battery & rectify it
- Increase current rating
- Check connection that is positive lead of charger to positive of battery & negative to negative
28-What are the reasons for overheating of battery while charging?
- Poor ventilation
- High charging rate
Lower specific gravity of electrolyte
29- What are the reasons for overheating of battery while discharging?
High discharge rate
Separators between plates have damaged
30-What are the reasons for cells having unequal voltages?
- Over discharge
- Lower electrolytes level
- Foreign material in electrolyte
- Positive plate worn out
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